Today, there are 7.3 billion mobile subscribers worldwide. It exceeds the 7.2 billion people of the world's population estimated by the US Census Bureau and is growing at 3% per year. The total number of smartphone users is 3.4 billion, which is expected to reach 6.4 billion by 2021. People use their smartphones for an average of three (3) hours a day. Of these, 20% spend time on phone calls and texts.